SSYTRI  -  compute the inverse of a real symmetric indefi­
       nite matrix A using the factorization A = U*D*U**T or A  =
       L*D*L**T computed by SSYTRF


SYNOPSIS

       SUBROUTINE SSYTRI( UPLO, N, A, LDA, IPIV, WORK, INFO )

           CHARACTER      UPLO

           INTEGER        INFO, LDA, N

           INTEGER        IPIV( * )

           REAL           A( LDA, * ), WORK( * )


PURPOSE

       SSYTRI computes the inverse of a real symmetric indefinite
       matrix A using the factorization  A  =  U*D*U**T  or  A  =
       L*D*L**T computed by SSYTRF.


ARGUMENTS

       UPLO    (input) CHARACTER*1
               Specifies whether the details of the factorization
               are stored as an upper or lower triangular matrix.
               = 'U':  Upper triangular, form is A = U*D*U**T;
               = 'L':  Lower triangular, form is A = L*D*L**T.

       N       (input) INTEGER
               The order of the matrix A.  N >= 0.

       A       (input/output) REAL array, dimension (LDA,N)
               On entry, the block diagonal matrix D and the mul­
               tipliers used to obtain the factor U or L as  com­
               puted by SSYTRF.

               On  exit,  if INFO = 0, the (symmetric) inverse of
               the original matrix.  If UPLO  =  'U',  the  upper
               triangular  part  of the inverse is formed and the
               part of A below the diagonal is not referenced; if
               UPLO  =  'L'  the  lower  triangular  part  of the
               inverse is formed and the  part  of  A  above  the
               diagonal is not referenced.

       LDA     (input) INTEGER
               The  leading  dimension  of  the  array A.  LDA >=
               max(1,N).

       IPIV    (input) INTEGER array, dimension (N)
               Details of the interchanges and the  block  struc­
               ture of D as determined by SSYTRF.

       WORK    (workspace) REAL array, dimension (N)

               = 0: successful exit
               <  0: if INFO = -i, the i-th argument had an ille­
               gal value
               > 0: if INFO = i, D(i,i) = 0; the matrix is singu­
               lar and its inverse could not be computed.


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